Due to the rapid developments of the information applications (IA) platform and the communication system as well as the development of the consumer electronics toward the trend of the “light-weight, thin, short and small” design, the development of the flexible circuit board (soft circuit board) is becoming more and more important. The conventional flexible circuit board is typically formed by a plastic substrate coated with copper foil. However, such a flexible circuit board usually cannot stand the heat generated from the operation of the high power electronic components mounted on the circuit board since the laminar structure of the circuit board can be delaminated due to the deformation of circuit board. Therefore, the conventional flexible circuit board faces the problem for the application of the high power electronic.
Meanwhile, it is well-known that the conventional circuit board with higher heat dissipation capability usually includes a metal plate having a relatively higher thermal conductivity as a lower layer, a circuit formed by the copper foil mounted on the metal plate, and an insulation layer made of the insulation paste, the insulation glass or the resin substrate being formed between the metal plate and the circuit. However, when such a circuit board is bent, the upper and the lower layers of the circuit board would be deformed by the compression stress and the tension stress respectively occurring thereon. Accordingly, a shear stress will occur at the bonded portion between the upper and the lower layers and cause the laminar structure of the circuit board being delaminated if the shear stress is larger than the bonded strength. Accordingly, the conventional circuit board with higher heat dissipation is not suitable for the flexibility application since the laminar structure can be damaged when the circuit board is bent.
Furthermore, please refer to FIG. 1, which shows a planar heat dissipation substrate disclosed in the U.S. Pat. No. 5,698,866. The planar heat dissipation substrate 100′ includes a heat sink 10′ and a heat spreader 20′ having a plurality of high power LEDs 35′ mounted thereon. With the design of such planar heat dissipation substrate 100′, the heat generated by the high power LEDs 35′ can be easily removed by the heat sink 10′ and the heat spreader 20′. However, the respective light paths projected from those high power LEDs 35′ will be almost perpendicular to the planar heat dissipation substrate 100′ since the planar heat dissipation substrate 100′ is not applicable for the flexible purpose. Moreover, please refer to FIG. 2, which shows a further optoelectronic device disclosed in the U.S. Pat. No. 5,660,461. As shown in FIG. 2, the conventional optoelectronic device 200′ is composed of a plurality of LED modules 45′ mounted on the heat dissipation substrate 40′. The heat dissipation substrate 40′ is formed by an electrically conductive and heat conductive metal base. Furthermore, a heat sink structure 43′ is attached on the lower side of the dissipation substrate 40′ while the LED modules 45′ are mounted on the opposite side of the dissipation substrate 40′, so as to form an LED array. As shown in FIG. 2, each of the LED modules 45′ has the latch structures 41′, 42′ in each side of the metal base for connecting with each other. However, although the latch structures 41′, 42′ can be used as a hinge for bending the LED array, it is obvious that the flexibility of such structure is still not good enough for many demanded applications. Moreover, such optoelectronic device structure is also complicated and costly since many components should be assembled together.
Based on the above, it is the main aspect of the present invention to provide a novel flexible circuit board which simultaneously has the flexibility and the heat dissipation ability and is suitable for the high power electronic application.